The present invention relates to a method for the preparation of 2,3,5-trimethylbenzoquinone or, more particularly, to an efficient method for the preparation of 2,3,5-trimethylbenzoquinone by the oxidation of 2,3,5- or 2,3,6-trimethylphenol in the presence of a specific catalyst.
As is known, 2,3,5-trimethylbenzoquinone is an important organic compound useful as a starting material in the synthetic preparation of vitamin E and other valuable chemicals. One of the conventional methods industrially undertaken for the preparation of 2,3,5-trimethylbenzoquinone includes the steps of sulfonation of 2,3,6-trimethylphenol as the starting material and oxidation of the sulfonation product by using manganese dioxide (see, for example, West German Patents No. 1,932,362 and No. 2,225,543) as an oxidizing agent. Although 2,3,6-trimethylphenol is an inexpensive material manufactured by the orthomethylation of m-cresol or by the oxidation of pseudocumene and available in any large quantities, the above mentioned manufacturing process of 2,3,5-trimethylbenzoquinone has problems in respect of the by-product to be disposed of as a waste material and the relatively high production cost.
Alternatively, it is also known that 2,3,5-trimethylbenzoquinone can be prepared by the direct oxidation of 2,3,5- or 2,3,6-trimethylphenol and many attempts and proposals have been made hitherto in connection with selection of the oxidizing agent and the catalyst for the oxidation reaction. Examples of the oxidizing agent proposed so far include nitric acid taught in Japanese Patent Publication 56-95145, perbenzoic acid taught in Japanese Patent Publication 59-39847, hypohalogenous acids taught in Japanese Patent Publication 60-81135 and the like. These methods also are not quite satisfactory as an industrial method in respect of evolution of toxic qases, expensiveness of the oxidizing agent and formation of by-products. It is also known that hydrogen peroxide can be used as the oxidizing agent and this method is the most promising as an industrial method because hydrogen peroxide is relatively inexpensive and the by-product formed from the oxidizing agent is water alone absolutely without problems of environmental pollution.
The oxidation reaction of 2,3,5- or 2,3,6-trimethylphenol with hydrogen peroxide to give 2,3,5-trimethylbenzoquinone is promoted by a catalyst and a method is known to use a salt of metal such as ruthenium and the like (see, for example, Chem. Lett., volume 24 (1983), page 5246 and European Patent Application 107176). This method is, however, disadvantageous due to the expensiveness of the rare metal as the constituent of the catalyst and relatively low yield of the desired product.